1. Field of the Invention
This invention refers to a method and an apparatus for classifying lumber pieces such as boards and planks in the sorting station of a saw mill.
2. Description of the Prior Art
The length sorting and the quality classification are executed in a sawmill in a sorting station, where for example three inspectors are working. Pieces of lumber pass in front of them through an inspection zone with their narrow ends towards the inspectors and under automatic rotation along their longitudinal axes so that both faces of the board can be inspected. Every inspector has to decide with each third piece at which length it shall be cut-off in a cutting station to achieve optimal economical result. The greater part of the tapering board which is cut off the higher is the quality of the remaining part but at the same time the greater is the waste and the lower the wood yield. The inspector must therefore in approximately one second, during which time the piece of lumber on a conveyor means passes before his eyes, decide on two in principle contradictory selections, and by pushing a button in a first selection apparatus, a push button set, give an order to the cutting station, and by pushing another button in a similar second selection apparatus give an order to the assortment station into which quality group the cut-off piece of lumber will be sorted. Generally, the cut-off part can be selected in a length equal to 0 to 5 feet. Assume for example a 3 feet length cut-off is ordered. The piece of lumber passes then, after the inspection zone, before a length measuring unit such as a series of photocells, where it is for example ascertained that the uncut piece is longer than 14, but shorter than 15 feet. The piece is then fed into a cutting station where it is cut to a length of 11 feet, i.e. 14 feet minus 3 times 1 foot minus the length-surplus over and above 14 feet because the final length is always adjusted to the nearest lower feet multiple.
Quality assortment is generally executed in four quality groups, viz: unsorted (US), fourth quality (IV), fifth quality (V) and sixth quality (VI). The highest quality is called unsorted and includes all lumber of the quality groups I, II, III and a limited part of the group IV, e.g. maximally 30% of the total of the US quality.
Into the fifth quality group belongs all lumber of the group V and the possibly remaining lumber of the quality IV.
The price relations between the quality groups vary with the state of the market. Neighbouring quality groups can for example differ with 20-30% in the case of pine and 10-15% in the case of spruce. In the high quality groups, price increases are proffered for low thickness, great widths and a special saw manner, so that the price relations sometimes can differ up to 50%.
Lumber pieces which become shorter than 9 feet are called "Stuage" and are paid only with 2/3 rds, if their share is great (e.g. according to an agreement more than 2 or 3% of the total wood volume). The cut-off waste is used for example for chippings for wood pulp production and the evaluation of such wood in relation to the lumber pieces has also great influence on the total economy of the sawmill production.
The inspector must thus in a time interval of one second--to make this interval longer would slow down the whole work rhythm of the mill--form an opinion on the optimal cut-off length, and by pressing a button in his say right hand selection apparatus (a set-up of push buttons) give via a control unit a corresponding order to the cutting station, and at the same time he must by pressing a button in his left hand selection apparatus (a similar set-up of push buttons) via the control unit give an order to the assortment station to group the cut-off piece in the compartment for a certain quality group. Both selections depend one on the other in accordance with the presently valid price relations between the quality groups.